If there is a significant difference in the audio, comparing LSB and
USB, the most likely reason is that the BFO frequencies for LSB and USB
are not adjusted properly. The Omni VI manual lists the correct
frequencies as 9.000000 MHz for LSB and 9.003000 MHz for USB. There is
an order in which the adjustments should be made, which is important,
because there are several trimmer capacitors and two crystals in the
BFO. Some of the capacitors are in the circuit all the time and some are
switched in by diodes only for some modes. If you do it in the wrong
order, you'll probably never get it right.
The 2.4 kHz wide 9 MHz IF filter in the Omni should cover the frequency
range of 9.000300 to 9.002700 MHz. When in LSB with the BFO running at
9.000000 MHz the low end roll off due to the filter is at 300 Hz. In USB
with the BFO running at 9.003000 MHz the low end roll off is also 300
Hz. Based on your description of the problem, I would say that your BFO
is running a frequency higher than 9.003000 MHz on USB. If it were
running at 9.003300 MHz, the low end roll off would be at 600 Hz instead
of 300 Hz. You would have less low end audio response.
By the way if you look at those numbers you'll realize that in the 9MHz
IF, when you are in LSB mode, the radio is generating and receiving USB
at 9 MHz. And in USB it operates on 9.003 MHz LSB. It gets flipped over
when it is mixed with the LO.
If the BFO frequencies are correct, the other possible cause of the
problem is some non-symetrical filter shape which might be caused by a
poor solder joint or a bad crystal in the 2.4 kHz BW 9 MHz IF filter.
This is much less likely than improperly adjusted BFO frequencies.
Don Wright wrote:
> Need to balance the transmit and receive audio on LSB and USB, right now my
> LSB is great full sound on transmit and receive, but on USB both transmit and
> receive are squeaky narrow, can someone tell me if there is a pot on the
> radio to adjust this and where it is located. 73.
> Don Wright WV4X
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